Titanium may be classified into two categories: commercially pure titanium (CP Ti), which is unalloyed and used in the chemical process industries and titanium alloys having alloying elements such as aluminium (Al) and vanadium (V) that are used for jet aircraft engines, airframes and other components.
Commercially pure titanium (CP Ti) is used within the chemical and medical industry because of its high corrosion resistance and biocompatibility and is defined within grades 1-4 whereof grade 1 is the purest with the lowest strength. Grades 2-4 are alloyed with increasing amounts of O, N, C and Fe and have higher strengths. Limiting factors for the usage of CP Ti are basically low yield strength (about 274 MPa) and low tensile strength (about 345 MPa).
It has been shown, in e.g. EP 2468912, that a significant improvement of tensile properties, such as yield strength and tensile strength has been achieved by deforming CP Ti at cryogenic temperatures but these improvements are not enough as there is no significant improvement in the ductility of the material. In highly demanding applications, such as medical implants and in chemical processing industries, it is desirable to have an object having a combination of high tensile strength and high ductility and thereby achieve long term sustainability and good fatigue properties.
Hong et al (Materials Science and Engineering 555 (2012) 106-116) discloses a process using a two dimensional cryogenic channel-die-compression (CrCDC) for deforming titanium, i.e. they are using compression stresses. In this a process, only plain strain will be introduced in the titanium during compression, which means that the microstructure will be sensitive to stress conditions after deformation, i.e. such as heat treatment.
Hence, there is still a need for a process that will provide a CP Ti product having a combination of high tensile strength and high ductility and good fatigue properties.